The regulation of pyruvate dehydrogenase in perfused heart and isolated heart mitochondria will be investigated. In the perfused heart pyruvate dehydrogenase flux will be monitored by measuring the decarboxylation of (1-14C) pyruvate in the effluent perfusate. Interconversion of pyruvate dehydrogenase between its active and inactive forms will be monitored by freeze-clamping the hearts with subsequent extraction and assay of active and total pyruvate dehydrogenase in the heart extract. The primary consideration to be investigated will be the relative conributions of product inhibition and active/inactive interconversion during changes in the metabolic state of the beating heart preparation.